Dielectric materials

ABSTRACT

A DIELECTRIC MATERIAL IS FORMULATED BY FIRING AN ADMIXTURE OF FROM ABOUT 2-55% BY WEIGHT ZIRCON (ZIRCONIUM SILICATE) AND ABOUT 45-98% BY WEIGHT OF A LEAD BARIUM BOROSILICATE GLASS. IN FINAL FORM, THE DIELECTRIC MATERIAL EXHIBITS A LOWER (APPROXIMATELY 6) AND A HIGH Q VALUE. THE PASTE COMPOSITION OF FORMULATED BY ADMIXING THE AFROEMENTIONED INGREDIENTS IN AN ORGANIC VEHICLE, DRYING THE PASTE AND FIRING THE PASTE AT A TEMPERATURE OF FROM ABOUT 800-1,000* C. THE PASTE IS USUALLY APPLIED VY A SCREEN PRINTING TECHNIQUE PREFERABLY USING A MESH SIZE IN THE RANGE OF ABOUT 165.

United States Patent Office 3,813,295 Patented May 28, 1974 3,813,295 DIELECTRIC MATERIALS Daniel W. Mason, West Peabody, Mass., and Henry H.

Nester, deceased, by Dianne L. Nester, special adminis- Itflatrix, Gloucester, Mass., assignors to Owens-Illinois,

No Drawing. Original application June 5, 1970, Ser. No. 43,941, now Patent No. 3,707,499. Divided and this application May 8, 1972, Ser. No. 251,447

Int. Cl. C04b 35/00; H01b 1/06, 3/02 US. Cl. 117-221 3 Claims ABSTRACT OF THE DISCLOSURE This is a division of application Ser. No. 43,941 filed June 5, 1970 and which issued Dec. 26, 1972 as US. Pat. No. 3,707,499.

This invention relates to dielectric materials. More particularly, this invention relates to dielectric pastes and materials made therefrom by thick film applications which are useful as capacitor dielectrics, crossover materials and multilayered dielectrics. 1

Dielectric materials most desirable for these described uses exhibit a low dielectric constant (K) and a high Q value. Q is the reciprocal of dissipation factor. Generally speaking, the art has turned to the area of devitrifiable glasses to achieve the necessary values of these desired properties. As is readily understood in the art, devitrifiable glasses have attendant therewith serious problems which affect both the technology and the economics of the system. That is to say, in order to form a devitrifiable glass into a dielectric material, a delicate time-temperature mechanism must be effected in order to change the glass from its amorphous or vitreous state into its crystalline or partially crystalline state. Such a delicate time-temperaturemechanism usually requires at least two heat delay steps which include a holding period at a nucleation,

producibility of the final product. A further problem with respect to these devitrifiable compositions is that when they are fired, they must go through a glassy state which tends to flow and therefore which, at least in part, destroys the resolution or definition of any printed lines into which the material is formed.

-It is a purpose of this invention to overcome the problems attendant with devitrifiable dielectric materials by providing the art with a unique dielectric composition which may be formed into a dielectric material having a low K and high Q value and which does not require that it be converted by devitrification techniques into a crystal line material in order to achieve the necessary values of these desirable properties. Rather, because of the uniqueness of this dielectric composition, it is quite able to withstand refiring without physical or electrical change and without exhibiting any substantial flow. Thus printed lines formed from the compositions of this invention maintain their resolution even after refiring. In addition, reproducibility is extremely high in view of the fact that the material is capable of being fired by a simple heat step at temperatures of about 800 to'1,000 C. or even retired at these temperatures.

The term fired as used herein is a term well-known in the art. This term is generally defined by the art as a heating step wherein sutficient heat is applied for a sufli cient period of time to change a particulate composition into a generally solid glass-like dielectric material.

Basically, the dielectric compositions contemplated by this invention comprise about 2-55% by weight of a ceramic powder, preferably zircon (zirconium silicate) with about 45-98% by weight of a lead barium borosilicate glass binder. While the particle size of the ceramic may range from about 0.1 to about 20 microns, it is preferable for the purposes of this invention to use an average particle size of zircon in the range of about 0.1-0.5 micron and still more preferably in the range of less than about 0.2 micron. Similarly, the particle size of the glass admixed'with the zircon to formulate the dielectric compositions of this invention may, before firing, be in a range of about 0.1 to about 20 microns but most preferably are provided in a range of approximately about 0.5-1.0 micron. By using the preferred ranges of average particle size as cited, a smooth film having the desirable low K, high Q values is insured.

Any well-known ceramic powder may be used which will render the resultant material a dielectric. Examples of such include A1 0 devitrified glass particles-zirconium silicates generally, including BaZrSiOg, MgZrSiO ZnZrSiO, and the like, TiO' and ZrO As stated, zircon (ZrSiO is preferred for purposes of this invention.

The dielectric compositions of this invention, as described, are most preferably useful as crossover dielectrics and thus, such a use contemplates a preferred use in accordance with this invention. Regardless of the use to which these' dielectric compositions are actually put, they are generally first formulated into a particulate blend and thereafter into a printing paste which is printed upon the desired area and fired into a dielectric glass-like material with or without a conductive source being present.

In order to form the pastes as described above, the basic admixture of powders of the glass binder and zircon particles in the appropriate particle sizes are dry blended and well mixed by adding them to a suitable organic car- .rier vehicle. For purposes of this invention, the preferred organic carrier vehicle which has found particularly good working characteristics in the subject environment consists of 2 /z% by weight-of ethyl cellulose admixed with anorganic thinner consisting of about 2 parts by weight butyl Carbitol acetate and 1 part by weight iso-amyl salicylate. -Any of the other conventional paste vehicles Well known in the art are also generally suitable and therefore may be employed if desired.

The paste may generally be formulated within a wide range of ingredients depending upon the ultimate useto An example of a particularly preferred paste composition in accordance with the teachings of this invention consists of 25.0% 'by weight of zircon having an average particle size of about 0.2 micron and from about 75.0% by weight'of a lead barium borosilicate glass consisting of 37% by weight SiO 10% by weight B 0 13% by weight Al O 15% by weight PbO, 2% by weight TiO and 23% by weight BaO. These ingredients are then admixed withv the above-described preferred vehicle in an ampuntby weight of 65.7% solids and 33 3 ,liquid ,organic carrier vehicle. In this preferred composition, the average particle size of the glass is about 0.7-0.9 micron.

For thick film applications, the above-described paste compositions are then printed by well-known screen printing' techniques such as by usinga screen mesh of prefer.- ably approximately 165 to 200 or greater. After the printing, which maybe a single printing, or. a double coat of the paste the dielectric material is air dried at a temperature of from about l C. to"125C. for a period ofifrom to 20 minutes. Temperatures "as low as room temperature with extended periods, of time'r'nay also'be used for drying. Afterdrying, the layer is .then subjected to a firing temperature ofiapproximately'SOO- 1000 C. and preferably about 875 C. for about 4-10 minutes and preferably about 5 minutes at peak tempera-i ture with 8 to 10 minute heat-up and cool-off periods. Films formedin accordance with theabove description generally have a; thickness of about 1.5 to 1.8 mils. Prob. erabl'y, .a typical, procedure, especially preferred for the purpose of this invention, may be illustratedas follows: Print' DryPrint+FirePrint--Dry+Apply Top Conductor.-'-Dry -Fire. The top conductor used ,may be of any, well-known type such as a paste'of vPd-Au, Pd Ag, and. the like admixed with a conventional organic carrier vehicle. Although it is preferred to fire the top conductor simultaneously withitsdielectric lamina, such is not necessary, and, if the situation dictates, it may be fired separately. Since the dielectric lamina of this invention, as described above, are reliable, no adverse effects result from separate firings.

As stated herein above, the dielectric materials formulated in accordance with the above exhibit extremely low K values and high Q values. K values may be as low as 4-6 and in any event are usually lower than 10. This represents a significant difierence over the prior art which generally is not able to obtain K values lower than about 11 or 1 2. In addition, the dielectric materials of ,this invention are inert to retiring cycles in that they retain their electrical properties and physical definitions upon refiring. The dielectric materials of this invention, furthermore, exhibit excellent dielectric strength usually greater than about 1,000 volts per mil and exhibit excellent screenability, definition and rheological shelf life. The Q factors generally achieved are very high comparable to the prior art and generally are represented in reciprocal by low dissipation factors (of less than about 0.002 at 25, C. and 1 kHz.). In addition, the materials are dense, fired structures which are extremely high in quality.

While the above materials have been described with respect to their usefulness as crossover dielectrics, it is also understood that they can be used in multisheet capacitance dielectrics as well as in multilayer materials. In the artof multilayer materials such as in the formation of hybrid multilayer dielectric boards and the like,

the property of solderability is usually a paramountimportauce. Solderability, as is well known, is the ability to solder a lead to a conductor which has previously been formed by firing it upon a dielectric layer. Solderability is usually negated by the dielectric, duringconductor firing, wetting the solderable surfaces of the conductor and thus. providing at such surfaces a material to which i a lead element cannot be soldered.

The dielectric materials of this invention may be used in multilayer devices which at the same time achieve solderability by altering the above-described procedure by which the conductors are fired on the dielectric material.

That is to say, the conductors are tired separately rather.-

than. simultaneouslyand at lower temperatures than those used to fire the dielectrics in order to prevent Wetting ofsolderability of the conductors in the devices are achieved. Thus, while the above procedure must be altered to the extent that the conductors must be fired separately and at lower temperatures than those at which the dielectric materials are fired so as to achieve solderability, the subject inventive concept still presents an important improvementover. the prior artwhich hadto rely upon. thdrlelicate mechanism of devitrification. to obtain a wonkable dielectric material.

The following examplesare presented bywayiof illustration rather thanlimitation. l I EXAMPLE 1 I A .dry blend is formulated consisting of by weight 251%;

zircon having an average particle size'of' about 0.2 0l8 micron and 75% ore 'glass" b'inder'consisting of 37% by weight SiO 10% by weight B 0 13% by weight A1 0 15% by weight PhD; 2% by weight TiO and 23% by weight B210 and having an average particle of about 1.0 micron. The dry blend is formed into a paste, by admixing 66.7 parts by weight thereof with33.3 partsby weight of a liquid organic vehicle consisting of 5%.: byweight ethyl cellulose and 95% by weight of athinner consisting of 2 parts by weight butyl Carbitol acetate' and 1 part by weight iso-amyl salicylate.

This paste is then printed over a previously formed conductor consisting of Pd-Au. Printing is accomplished by using a screen printer having a mesh size of 165 and applying three coats of the paste with a drying period of 15 minutes at about 125 C. between two coats.

A. Pd-Au paste conductor is formulated by admixing particles-of a Pd-Au conductor powder having an average particle size of 2-3 microns and consisting of 70.4% by weight Au, 17.6% by weight Pd, 8.0% by weight Bi O and 4.0% by weight of a glass binder consisting of 17.6% by weight SiO 16.0% by weight B 0 0.4% by weight A1 0,; 60.0% by weight P'bO; and 5.9% by v weight CdO; with a liquid organic vehicle consisting of 20% by weight ethyl cellulose and 80% by weight thinner consisting of 2 parts by weightbutyl 'Carb-itol acetate and 1 part by weight iso-amyl salicylate. The paste is formulated of 75% by weight Pd-Au powder and 25% by weight liquid organic vehicle.

The conductor paste is then screen printed over the previously screened and dried dielectric layer by using a screen mesh of 200. The conductor layer is then dried similarly as the dielectric layer.

The composition consisting of the dielectric layer and the conductor layer is now fired at a temperature of 875 C. at peak for 5 minutes with 8 minute heat-up and cool-down periods. The resultant composite consists of two conductors having interposed therebet-ween an insulating crossover dielectric lamina exhibiting a dielectric constant of about 6 and a reciprocal Q value (i.e.

dissipation factor) of less than 0.002 at 25 C. and 1 kHz. The crossover dielectric lamina during firing wetted the upper conductor rendering it nonsolderable.

EXAMPLE 2 'printing a top conductor thereon, was then fired at a the now fired dielectric. In order to obtain a .solderable.

C. and should preferably be as low as conductor firing will allow. When this is accomplished, extremely useful dielectrics in multilayer devices which allow for the temperature of 875 C. at peak for 5 minutes with 8 minute heatup and cool-down periods.

Thereafter, the conductor of Example is printed and 0 dried as described in the aforementioned example over (bendable) upper conductor, the printed and dried conductor composition is then fired at a temperature of 700? C. which is significantly below the firing range of the fired dielectric lamina. The resulting composite exhibits the same effective dielectric propertiesas described in Example 1. In addition, an electric lead soldered to the upper conductor forms a tenacious bond therewith thus indicating that the solderability of the surfaces of the upper conductor has been maintained. By such a procedure, it can be seen that the top conductor of a multilayered dielectric may always be maintained in solderable condition even though intermediate conductor layers became wetted when firing the next dielectric lamina thereupon.

Once given the above description, many other features, modifications and improvements will become apparent to the skilled artisan. Such features, modifications and improvements are therefore considered to be a part of this invention, the scope of which is to be determined by the following claims.

We claim:,

1. In the method of making an electronic device which comprises printing a substrate with a dielectric component, the improvement in which said dielectric component comprises a printable dielectric paste composition comprising 2-55% by weight of powdered zircon having a particle size of about 0.1 to about 0.5 micron and 45-98% by weight of a powdered lead barium borosilicate glass binder having a particle size of about 0.5-1.0 micron, said 6 paste composition being fireable at a temperature in the temperature range of 800-1,000 C. to form a refireable dielectric possessing a dielectric constant (K) of less than 10 and a dissipation factor of less than about 0.002 at C. and 1 kHz.

2. The method of claim 1 wherein said composition consists of 25% by weight zircon and by weight of said glass binder.

3. The method of claim 1 wherein said lead barium borosilicate glass consists of by weight: 37% SiO 10% B 0 13% A1 0 IS,% PbO, 2% Ti02, and 23% BaO.

References Cited UNITED STATES PATENTS 3,673,092 6/1972 Dietz 10649 ALLEN B. CURTIS, Primary Examiner M. L. BELL, Assistant Examiner US. Cl. X.R. 10649, 53 

